Positron Emission Computed Tomography (PET) technology is a nuclear medical clinical imaging technology. A positron emitted from radionuclides injected into an intro-subject (a human body as an example in the followings) is combined with a negatron within the human body to generate annihilation radiation after movement of nearly 1 mm to produce two γ photons with the same energy but in opposite directions. A PET apparatus detects the γ photons through a detector including crystal arrays. When the γ photons touches crystals of the crystal arrays during the movement of the γ photons, the touched crystals can sense energy data of the γ photons. Since a low energy captured by the detector, an energy spectrum of lesion may be attained through amplifying the energy and processing the amplified energy. The energy detected by the detector is generally amplified through a Variable Gain Adjust (VGA) apparatus connected with the detector. The higher an amplified gain of the VGA apparatus, corresponding magnification of the energy is increased.
Currently, a new type of photomultiplier, which is Silicon photomultiplier (SiPM), is constituted of hundreds to tens of thousands of cell arrays of avalanche photo diode (APD) with a diameter of several to several tens of micrometers and integrated on a single silicon wafer. As a very small size of SiPM, one SiPM may be connected with one crystal to form a SiPM detector having 1:1 configuration. The SiPM in this configuration may detect single γ photon through one crystal thereof, and since generally the SiPM detector has one crystal, location of the crystal receiving the γ photon may be determined once the energy data are detected by the SiPM detector. Thus, SiPM is capable of applying in the PET apparatus as a detector thereof.